Chapter 6

PHP

Interacts

with Mysql Database

IntroductionIn PHP, there is no consolidated interface. Instead, a set of library functions are provided for executing SQL statements, as well as for managing result sets returned from queries

We overview these functions here and show how they can be combined to access the MySQL DBMS.

PHP provides support for MySQL through an array of functions that can be used to manipulate MySQL data.

The purpose of this tutorial is to introduce those functions commonly used in PHP data-driven applications for retrieving, updating, inserting, and deleting data.

Since PHP 5 there are two interfaces available for MySQL programming: The mysql functions are known to many PHP programmers from earlier versions of PHP. New since PHP 5 is the object- oriented interface mysqli, which enables more elegant programming features and access to new MySQL functions

mysql FunctionsThe mysql functions are not an integral part of PHP, but an extension.

In order for this extension to be used, PHP under Linux must have been compiled with the option —with-mysql. With the Windows version of PHP, the corresponding extension is provided as a DLL. However, the extension must be activated

in php.ini: extension=php_mysql.dll A.) Establishing a Connection

To establish a connection, execute mysql_connect, where you need to pass three pieces of information: the computer name (hostname) of the MySQL server, the MySQL user name, and the password. If MySQL is running on the same computer as the PHP script, the computer name should be localhost.

$conn = mysql_connect("localhost", "username", "xxx");

mysql FunctionsA.) Establishing a Connection

The function returns an identification number. You will need this number in the future only if you open more than one connection to MySQL. (As long as there is only one connection to MySQL, this connection is the default connection. The ID number therefore does not need to be given in calling various mysql_xxx functions.)

If you wish to provide the PHP code for establishing the connection itself with a readable error message, the necessary code looks something like this:

$conn = @mysql_connect("localhost", "username", "xxx");

if($conn == FALSE) {

echo "<p>error message ...</p>\n";

exit();

}

mysql FunctionsA.) Establishing a Connection

As soon as a connection has been made, you can execute SQL commands with various mysql_xxx functions.

you can select a default database with mysql_select_db. (This corresponds to the SQL command USE databasename.)

mysql_select_db("mylibrary");

You close the connection to MySQL with mysql_close.

Mysql_close(connection_id);

mysql FunctionsB.) Executing SQL Commands

To execute SQL commands, you pass them as a character string to the function mysql_query. If the command is not intended for the current database, you can add the name of the desired database using mysql_db_query.

With both of these functions an optional final parameter can be given: the ID number of the connection (that is, the return value of mysql_connect) if there is more than one

connection to MySQL.

$result = mysql_query("SELECT COUNT(*) FROM titles");

$result = mysql_db_query("mylibrary", "SELECT COUNT(*) FROM titles");

Every type of SQL command can be executed with mysql_query: queries with SELECT; changes to data with INSERT, UPDATE, and DELETE; changes to the database structure with CREATE TABLE; etc.

mysql FunctionsB.) Executing SQL Commands

If an SQL command can be correctly executed, mysql_query returns a nonzero value. If the command involved a query, the return value of mysql_query is a reference to a PHP resource (e.g., a character string of the form “Resource id #2”).

The return value can be used in various other functions (e.g., mysql_fetch_row) to evaluate individual fields of the table.

On the other hand, if an SQL command cannot be executed, mysql_query returns the result FALSE (i.e., 0)

C.) Evaluating SELECT ResultsWhen you execute a SELECT query with mysql_query, you obtain as result a reference to a table with rows rows and cols columns:

$result = mysql_query("SELECT * FROM titles");

$rows = mysql_num_rows($result);

$cols = mysql_num_fields($result);

C.) Evaluating SELECT ResultsIt is much more efficient to evaluate the result row by row. For this there are three functions:

$row = mysql_fetch_row($result);

$row = mysql_fetch_array($result);

$row = mysql_fetch_assoc($result);

$row = mysql_fetch_object($result);

• mysql_fetch_row returns a record in the form of a simple array. Access to the

columns is via $row[$n].

• mysql_fetch_array returns a record in the form of an associative array.

Access to the columns is via $row[$n] or $row[$colname] (so, for example,

$row[3] or $row[“publName”]). The column name is case-sensitive.

• mysql_fetch_assoc (available since PHP 4.0.3) also returns an associative

field, which can be read in the form $row[$colname]. In contrast to

mysql_fetch_array, one is not allowed to give the column number as parameter.

• mysql_fetch_object returns a data record as object. Access to the column is via

$row->colname.

C.) Evaluating SELECT Results

A common feature of all four functions is that with each call, the next record is automatically returned (or FALSE if the end of the list of data has been reached

PHP stores query results until the end of the script. If a query result must be released earlier (for example, if you have executed a large number of queries in a script and don’t want to waste memory), you can release the result early with mysql_free_result. This is particularly useful if the script contains a loop that executes SQL queries.

mysql_free_result($result);

mysqli FunctionsThe mysqli interface is considered, at least by developers of MySQL applications, to be among the most important innovations in PHP 5. This interface makes possible object-oriented programming of database access with MySQL and is thus a great help in the creation of readable code.

The mysqli interface is, like the mysql interface, not an integral component of PHP, but an extension. For this extension to be usable, PHP must be compiled under Linux with the option —with-mysqli. With the Windows version of PHP the corresponding extension is provided as a DLL, and the extension must be activated in php.ini: extension=php_mysqli.dll

A.) Connecting to the Database

The first step in any database transaction from PHP is connecting to the database. When you're using MySQL directly, this is analogous to executing the MySQL client application; however, in PHP this is done by using the mysqli_connect() function. The syntax for this function is as follows:

mysqli_connect([$hostname [, $username [, $password [, $dbname ]]]]);

mysqli FunctionsB.) Selecting a Database

After a connection has been created, the mysqli_select_db() function can be used to select the current database in the same way the USE SQL command was used from the client. The syntax for the mysqli_select_db() function is as follows:

mysqli_select_db($link, $dbname);

C.) Performing a Basic Query Now that we know how to connect to a MySQL server and select a database to use, it's time to start performing SQL queries against it. To perform queries, we will use the mysqli_query() function with the following syntax:

mysqli_query($link, $query );

mysqli FunctionsD.) Fetching Resultset Rows

When performing queries that modify the tables within a database, such as INSERT and UPDATE, generally there is no data to return from the database. However, queries such as SELECT, which retrieve data from the database, require that data must somehow be accessed from within PHP.

When returning the results from a resultset into PHP, various options are available, each providing a unique usefulness depending on the circumstance.

The most general of the result-retrieving functions is the ysqli_fetch_array() function. The syntax for this function is as follows:

mysqli_fetch_array($result [, $array_type])

MYSQLI_ASSOC:Return an associative array.

MYSQLI_NUM:Return an enumerated array.

MYSQLI_BOTH:Return both an enumerated and associative array.

Note:If no value is provided, the MYSQLI_BOTH constant is the default value.

mysqli FunctionsE.) Counting Rows and Columns

Often, it is useful to know how many rows or columns exist for a given resultset. For these purposes, MySQLi provides the mysql_num_rows() and mysqli_num_fields() functions, whose syntax follows:

mysqli_num_rows($result)

mysqli_num_fields($result)

F.) Freeing ResultsAfter a query is performed, the resultset for that query is stored in memory until the PHP script that performed the query is terminated. Although generally this is acceptable, when you are working with large resultsets, it becomes important to free the resultset in memory. This can be done using the mysqli_free_result() function as follows:

mysqli_free_result($result)

mysqli FunctionsG.) Closing the Database Connections

Although PHP will automatically take care of closing any outstanding database connections (as appropriate), a connection to a database can be explicitly closed using the mysqli_close() function with the following syntax:

mysqli_close($link)

The end of Chapter 6

Thanks for your paying attention